Observation of Si(001) surface topography at temperatures below 1140t°C using a reflection electron microscope

Abstract

The changes in the surface topography of a Si(001) vicinal sample caused by heating it to temperatures below 1140t\ifmmode^\circ\else\textdegree\fi{}C by direct current are investigated by reflection electron microscopy: the surface normal of the sample is misoriented by less than 2\ensuremath{'}. At temperatures below 1000t\ifmmode^\circ\else\textdegree\fi{}C, the surface is mostly covered by preferential terraces (for example, 2\ifmmode\times\else\texttimes\fi{}1 terraces) determined by the direction of the heating current. At temperatures below about 850t\ifmmode^\circ\else\textdegree\fi{}C, pairs of steps are uniformly distributed on the surface, while step bands are formed by the aggregation of steps at temperatures near 950t\ifmmode^\circ\else\textdegree\fi{}C. A few wide terraces remain between the step bands: in our sample, they are about 5 \ensuremath{\mu}m wide in the direction parallel to the current. At temperatures between 1000t\ifmmode^\circ\else\textdegree\fi{}C and 1100t\ifmmode^\circ\else\textdegree\fi{}C, the step bands relax and the narrow terraces (1\ifmmode\times\else\texttimes\fi{}2 terraces) widen due to the evaporation of Si atoms. At temperatures between 1070t\ifmmode^\circ\else\textdegree\fi{}C and 1100t\ifmmode^\circ\else\textdegree\fi{}C, atomic steps appear due to the relaxation in pair steps; both the 2\ifmmode\times\else\texttimes\fi{}1 and 1\ifmmode\times\else\texttimes\fi{}2 terraces coexist with approximately equal widths (about 1 \ensuremath{\mu}m). At temperatures above 1100t\ifmmode^\circ\else\textdegree\fi{}C, the surface topography changes to one composed of mosaic domains due to the evaporation of the atoms. For the Si(001) vicinal surface, the evaporation temperature of Si atoms is about 1000t\ifmmode^\circ\else\textdegree\fi{}C for Si atoms released from the ${\mathrm{S}}_{\mathrm{b}}$ step and about 1100t\ifmmode^\circ\else\textdegree\fi{}C for the atoms released from the ${\mathrm{S}}_{\mathrm{a}}$ step, where the evaporation temperature is determined by the activation energy, which consists of the release energy and the evaporation energy.